Device for preheating a component cooled by  conduction and/or by convection

ABSTRACT

The present invention relates to a device for preheating a component cooled by conduction and/or by convection. The component is in contact with a heat conductor and the device includes a heater to heat the part, the device further including at least one heat pipe having fluid within, to connect a heat dissipater with the heat conductor, the dissipater and the part furthermore being thermally insulated from one another. Freezing of fluid in the heat pipe facilitates preheating of the component at low temperature. The invention applies notably to the starting of components subjected to low temperatures, for example, components installed in systems on board aircraft.

The present application claims the benefit of French Patent Application Serial No. 0801483, filed Mar. 18, 2008, which is hereby incorporated by reference in its entirety.

The present invention relates to a device for preheating a component cooled by conduction and/or by convection. The invention applies notably to the starting of components subjected to low temperatures, for example components installed in systems on board aircraft.

Electronic components, for example computer processors, are designed to operate in a limited temperature range, for example between 0° C. and 100° C. Therefore, when these components operate, they give off a quantity of heat which must be cleared away in order to avoid exceeding the authorized top temperature limit. The calories generated by the component are then usually cleared away thanks to means of cooling by conduction or by convection.

In certain situations, notably in a large number of onboard systems, the components are placed in environments at low temperatures—for example −40° C. The starting of these components at temperatures below their bottom operating temperature limit poses a problem. In order to raise the temperature beyond this bottom limit, it is possible for example to place a heating resistor close to the component. But the cooling means that are present in order to clear away the excess calories will oppose the action of this heating resistor, thereby slowing, or even totally nullifying its effect. There is therefore a contradiction between the need, when cold, to preheat the component before starting it, and the need, when hot, to clear away the calories generated by the component.

As an example, taking as the hypothesis a conduction-cooled 15 W dissipation processor, it is necessary to preheat the processor with 74 W of power for 9 minutes in order to bring its temperature from −40° C. to 0° C. This waiting time is often too long and this required power is usually too high to be acceptable in onboard equipment.

An object of the invention is to allow a component associated with cooling means to start in an environment the temperature of which is below its minimum operating temperature. Accordingly, the subject of the invention is a device for preheating a component in contact with a heat-conducting part, the device includes means for heating the said part, the device being characterized in that it includes at least one heat pipe connecting a heat dissipater with the said part, the said dissipater and the said part furthermore being thermally insulated from one another.

By preventing the clearing away of the calories by an effect of freezing the fluid inside the heat pipe, the device according to the invention makes it possible to rapidly raise the temperature of the component in order to bring it to an acceptable level before it is started. Preferably, the volume of the heat-conducting part is small, so as to limit the energy used to preheat the component.

The heat-conducting part may be formed by an excrescence of the heat pipe, so as to reduce the volume of material to be heated and to enhance the efficiency of conduction between the heat pipe and the heat-conducting part.

According to an embodiment of the device according to the invention, each end of the heat pipe is placed in contact with the heat dissipater, the central portion of the heat pipe being in contact with the heat-conducting part. This embodiment makes it possible to generate substantially symmetrical heat-clearing paths, which facilitates the heat conduction, notably when the device sustains accelerations hampering the movement of the fluid contained in the heat pipe.

The heating means may include at least one heating resistor, the said resistor being placed adjacent to the heat-conducting part.

Advantageously, the heat-conducting part and the heat pipe are insulated in order to limit the heat loss.

In addition, the heat-conducting part may be rounded on the surface in order to reduce the heat loss by radiation.

Preferably, the heat-conducting part and the heat pipe are made of low specific heat materials, such as, for example, aluminium or copper.

According to an embodiment of the device according to the invention, the heat-conducting fluid used in the heat pipe may be chosen so that its solidification temperature is at least equal to or slightly below (for example a few degrees Celsius less) the preheating temperature to be achieved.

The device according to the invention may for example be installed in an onboard system greatly limited in available power and subjected to low temperatures.

Other features will appear on reading the following detailed, non-limiting description given as an example with respect to the appended drawings which represent:

FIG. 1, a top view of an embodiment of the device according to the invention;

FIG. 2, a view in longitudinal section of the embodiment of FIG. 1;

FIG. 3, a view in cross section of the embodiment of FIG. 1;

FIG. 4, a view of the heat-conducting part used in the embodiment of FIG. 1.

The same reference numbers in various figures designate the same elements.

FIG. 1, FIG. 2 and FIG. 3 show respectively a top view, a view in longitudinal section and a view in cross section of an embodiment of the device according to the invention.

The device 100 of the example includes a component 102 placed on a substrate 104, which substrate 104 is placed on a printed circuit board 106. A heat-conducting part 108, for example an aluminium block, is placed in contact with the component 102. In the example of FIGS. 1, 2 and 3, the conducting part 108 is placed adjacent to the top face of the component 102.

Furthermore, a heat dissipater 110, for example an aluminium drain, is clamped by cold plates 112 a, 112 b and placed close to the component, without touching it. In addition, all contact should be avoided between the conducting part 108 and the heat dissipater 110 so that no direct heat path between the conducting part 108 and the heat dissipater 110 is created. In the example, the heat dissipater 110 is a plate that is perforated so that the conducting part 108 can pass through without touching the plate.

The heat dissipater 110 should make it possible to clear away a large proportion of the calories generated by the component 102. Therefore, a heat pipe 114 connects the heat dissipater 110 to the conducting part 108 so that the heat pipe 114 establishes an efficient heat-conducting path between the part 108 and the heat dissipater 110 when the temperature of the heat pipe 114 is high enough to allow the fluid contained in the heat pipe 114 to leave the solid phase and to operate a heat-conducting circuit. On the other hand, when the temperature of the heat pipe 114 is too low to allow the fluid to melt, the heat-conducting circuit inside the heat pipe 114 is impossible, which thermally insulates the conducting part 108 from the heat dissipater 110. In the example, the top face of the heat dissipater 110 is grooved 111 to the dimensions of the heat pipe 114 and the heat pipe 114 is placed in the groove 111, the area of contact between the heat pipe 114 and the heat dissipater 110 thereby being maximized.

In order to raise the temperature of the component 102, a heating resistor 116 is placed close to the latter. In the example, the heating resistor 116 is placed adjacent to the conducting part 108, but in another embodiment, the heating resistor 116 is placed on the heat pipe 114.

The heat-conducting part 108 notably plays a role of a heat interface. Specifically, on the one hand, it carries the calories originating from the heating resistor 116 to the component 102, and on the other hand, when the component 102 is operating, the heat-conducting part 108 carries the calories originating from the component 102 to the heat pipe 114. According to one embodiment, the heat-conducting part 108 is only an excrescence of the heat pipe 114, the said excrescence 108 being fashioned at the time of manufacture of the heat pipe 114.

When, initially, the device 100 is subjected to an ambient temperature that is lower than the solidification temperature of the fluid contained in the heat pipe 114 (at the internal pressure of the heat pipe 114), the heating resistor 116 transmits calories to the heat-conducting part 108, hence to the component 102 and the heat pipe 114. Since the fluid contained in the heat pipe 114 is solidified, the heat pipe 114 is inoperative; therefore, the calories remain largely confined to the assembly formed from the component 102, the heat-conducting part 108 and the heat pipe 114. The temperature of this assembly increases until it reaches the minimum operating temperature of the component 102. The component can then be started without risk, then when the temperature of the assembly {component 102, conducting part 108, heat pipe 114} reaches or even exceeds the melting temperature of the fluid, then a heat-conducting circuit can be made in the heat pipe 114, which then carries away the received calories to the heat dissipater 110, thus preventing the component 102 from overheating.

The fluid used in the heat pipe 114 is, for example, water. However, fluids with different solidification temperatures may be chosen in order to suit the conditions of use of the device 100. For example, for components operating at very low temperatures, alcohol may be a judicious choice for the heat pipe 114. Whatever fluid is chosen, its solidification temperature should be below the maximum operating temperature of the component 102.

In the example, each end of the heat pipe 114 is placed in contact with the heat dissipater 110, the central portion of the heat pipe 114 being in contact with the conducting part 108. Therefore, the heat pipe 114 of the example includes an evaporator on the conducting part 108 and two condensers, one at each end of the heat pipe 114. This configuration results in obtaining two substantially symmetrical heat clearance paths, which reduces the distance of travel of the fluid from a condenser to the evaporator and consequently makes it easier to establish a heat circuit. Notably, this configuration improves the heat-conducting path brought about by the heat pipe 114 when the device 100 sustains accelerations—including natural gravitation—hampering the movement of the fluid.

According to another embodiment, a first end of the heat pipe 114 is placed adjacent to the conducting part 108, whereas its second end is placed in contact with the heat dissipater 110, this configuration resulting in a simple evaporator-condenser circuit.

FIG. 4 shows a view of the heat-conducting part used in the embodiment of FIG. 1.

The conducting part 108 of the example is in the form of an arch. In other words, it is a parallelepiped of which one face 401 has been hollowed out to form a groove 410 to the dimension of the heat pipe 114. The face 402 opposite to the hollowed-out face is placed in contact with the component 102 (FIGS. 1, 2, 3) and a side face 403 includes a sufficient area to place a heating resistor thereon.

According to another embodiment of the device according to the invention, the conducting part 108 may be made in many ways, provided notably that the shape chosen allows good heat conduction between the said part 108, the heat pipe 114 and the component 102. Furthermore, several heating resistors may be placed adjacent to the conducting part 108 in order to more rapidly raise its temperature.

To take the example cited in the preamble of this application, with a temperature of approximately −40° C. and a conduction-cooled 15 W dissipation processor, the use of a device according to the invention makes it possible to reduce the power needed to be supplied to 20 W and the preheating time to 40 seconds in order to bring its temperature from −40° C. to 0° C., compared with 74 W and 9 minutes that are necessary with a conventional device, which represents approximately a gain (time×power) with a factor of 50.

The device according to the invention may be used to bring a component to its minimum specified temperature, for example 0° C., before it is powered up or before it is initialized. Nevertheless, if the available power is very low and/or the acceptable, time for preheating is very short, the device may also used to bring the component to a temperature below the specified temperature, for example −20° C.,—but all the same higher than the ambient cold temperature—40° C. This limited rise in temperature may in effect be sufficient to achieve an acceptable success rate during a cold sorting of the card fitted with the component.

The device according to the invention preferably applies to the electronic components present on cards cooled by conduction. However, without departing from the context of the invention, the device may equally apply to cards cooled by convection considering that a cold wall may be formed by a convection radiator associated with the component. 

1. A device for preheating a component, the device comprising: a heat conductor in thermal contact with the component; a heater to heat the heat conductor; at least one heat pipe in thermal contact with the heat conductor, the at least one heat pipe having a solid phase that is thermally nonconductive, and a fluid phase that is thermally conductive; and a heat dissipater in thermal contact with the at least one heat pipe, the heat dissipater being thermally insulated from the heat conductor when at least one heat pipe is in the solid phase.
 2. The device according to claim 1, wherein the heat-conducting part comprises an excrescence of the heat pipe.
 3. The device according to claim 1, wherein the heater comprises at least one heating resistor placed adjacent to the heat conductor.
 4. The device according to claim 1, wherein the heat pipe further comprises: a first end portion; a central portion adjacent to the first end portion; and a second end portion adjacent to the central portion, the second end portion opposite from the first end portion, wherein the first end portion and the second end portion are in physical contact with the heat dissipater, and the central portion is in physical contact with the heat conductor.
 5. The device according to claim 1, wherein the heat conductor and the heat pipe are insulated in order to reduce the heat not conducted to the heat dissipater.
 6. The device according to claim 1, wherein a surface of the heat conductor is rounded in order to reduce the heat loss by radiation.
 7. The device according to claim 1, wherein the heat conductor and the heat pipe comprise low specific heat materials.
 8. The device according to claim 1, wherein the heat pipe further comprises a heat-conducting fluid having a solidification temperature at least equal to or slightly below a predetermined preheating temperature. 